Ok, but I doubt the money you spend to insulate the sealed attic from the conditioned living space at the ceiling would ever be recouped in energy savings.

Forgive me if I missed this, but what is your current insulation status and what are you trying to accomplish?

I have owned two older houses in Houston and can offer the following observations.

In a vented attic with insulation in the ceiling, the attic space will be at or above (due to solar) outdoor ambient in the summer and above outdoor ambient in the winter unless the sun is out.

On a hot, summer day, the attic can easily be >120°, and that holds a LOT of moisture.  If you have old blown fiberglass insulation and the AC set low, that humidity will find its way into the insulation and at some point condense.  You may not have moisture condensing on your drywall ceiling, but your insulation probably looks nasty.

I am guessing you probably have a vented attic and some sort of blown insultation above the ceiling and no vapor barrier.  Are you removing the old insulation?

If not, adding a (vented) radiant barrier at the roof framing (preferably leaving an air gap) will probably the most cost effective along with perhaps "touching up" the old insulation where it has been moved/removed.

If you are "starting over", I would go with spray foam (either open or closed) and make a sealed attic as long as your roof is in good repair. 

Bruce

Bruce . . .

Thank you for your input.

This is a small custom home built in 1974 (in a track home fashion from what I can tell). It is 1800 square feet with an unattached two-car garage. The remodel plan includes removing all sheetrock in the home and re-installing studs (before OSHA and drug/alcohol testing -- need I say more), floorplates, and reinforcing some load areas with steel. It is a complete remodel floor to roof (without a new roof at this time, which is covered in black shingles and is in very good shape). You are correct on the blown insulation and it is compacted to nothing -- there are bare spots in several places. Since I am originally from far North -- having lived in Calgary, North Dakota, Montana and am building a new build in the Black Hills of South Dakota, I am completely unfamiliar with "southern, hot, humid" insulating.

The attic has no radiant barrier, very little insulation as I described, vents in the underside of the eaves, and turbines for circulation. The roof is a 4 / 12 ptich roof. We use the attic for storage (particularly the long run where one can actually stand upright) and have no plans to build it out for additional living space. We have already decided to get ridge vents installed and eliminate the turbines. Our goals for this home are to keep it and bring it up to todays standards for energy efficiency. Less energy use = lower utility bills. And, we are interested in any steps that would provide tax benefits now and recouping costs through lower energy bills in the short future.

That sounds a lot like the house we had in the Memorial (Wilcrest/Kirkwood) area!  Construction quality was usually horrible  at that time in Houston.

Since you are doing major work, I would seriously consider sprayfoam for the walls and roof (making a sealed attic).  This is what I would do for a new wood framed house.  The sprayfoam will also provide some additional structural strength.  While you have everything opened up, review and consider reinforcing the roof to wall connections, as this is usually one of the failure points in very high wind (tornado) conditions.

Some caveats, however.  Remember that there is not always a perfect solution.

1.  If you use spray foam, you will go from a very (air) leaky house to a very (air) tight house.  You will probably want to install an ERV for ventilation.

2.  When (not if) water leaks in the walls or roof, is there a way for it to dry?  Today, you probably have no effective air or vapor barrier, so any leaks likely have the possibility to dry without rotting the structure.  This is probably more of a concern with your roof than the walls.  I would not worry too much about leaks from 5 or 10 year events like hurricanes, but trapped moisture can be a problem and there may be a lot of leaks that only manifest themselves in severe events.

If you don't have complete confidence in your roof, put the spray foam at the ceiling stay with a ventilated attic.

Joseph Lstiburek's books on Hot Humid Climates and Water Management Guide are great sources of information.

Good luck,

Bruce

There are several studies published about the pros and cons of vented attics at http://www.insulationspf.com and biobased.net. Most the comments are quite useful, I would add though that no matter what you do, especially in your area of Texas, do not leave a combination of attic floor fiberglass with sprayfoam lid (closed or open cell). You'll get one heck of an oven effect going if you do.